1. Field of the Invention
The present invention relates to a front light, a reflective type of display and a light controlling method in the front light.
2. Description of the Prior Art
FIG. 1 shows a schematic sectional view of a reflective type of liquid crystal display 1 comprising a front light 2 and a reflective type of liquid crystal display panel 3. According to the reflective type of liquid crystal display 1 using the front light 2, the light emitted from a light emission surface 6 of the front light 2 is roughly divided into two. That is, one is image light 8 which is emitted from a linear light source 4 such as a cool cathode ray tube, propagated in an optical waveguide 5, emitted almost vertically from the light emission surface 6, passes through a glass substrate and a liquid crystal layer of the liquid crystal display panel 3, reflected by a reflection surface 7 to the original position, passes through the liquid crystal display panel 3 and the front light 2, and then emitted toward an viewer as shown by an arrow of a solid line in FIG. 1. The other is noise light 9 which is reflected by the light emission surface 6 of the front light 2 or a glass substrate surface of the liquid crystal display panel 3 and emitted to the viewer as shown by an arrow of a broken line in FIG. 1.
When the noise light 9 is generated, as shown in FIG. 1, since the image light 8 and the noise light 9 is emitted in the same direction, white light overlaps with the image generated by the liquid crystal display panel 3, causing a contrast of a screen and visibility to be lowered.
FIG. 2 shows a schematic sectional view of a reflective type of liquid crystal display 10 provided so as to prevent the visibility from deteriorating. According to this reflective type of liquid crystal display 10, patterns 11 having sections in the shape of cutting blade are formed on the surface (the surface opposed to the light emission surface 6) of the optical waveguide 5 parallel to the light source 4 (vertical to the light), and the light propagated in the optical waveguide 5 is totally reflected by the pattern 11 and emitted from the light emission surface 6 of the optical waveguide 5 in the oblique direction. Therefore, even when the light emitted from the light emission surface 6 is reflected by the light emission surface 6, or the light emitted from the light emission surface 6 is reflected by the surface of the liquid crystal display panel 3, the noise light 9 (regular reflection light) is emitted to the viewer in the oblique direction and it is not likely to be directly input to the eye of the viewer. Therefore, the noise light 9 in the front screen direction is reduced and the contrast of the screen is improved. Since the light emitted from the light emission surface 6 in the oblique direction passes through the liquid crystal layer of the liquid crystal display panel 3 and then reflected by the reflection surface 7 having an appropriate inclination angle in the vertical direction and becomes the image light 8 in the front screen direction, brightness in the front screen direction can be maintained and the visibility is improved.
The structure of the optical waveguide shown in FIG. 2 can be employed in a case a linear light source comprising a cool cathode ray tube, a waveguide rod or a plurality of point light sources is used as the light source of the front light. However, when the point light source is used, since the light emitted from a point light source 12 radiates from the point light source 12 in the optical waveguide 5 as shown in FIG. 3, the directions of the light reflected by the patterns 11 having the shape of cutting blade and emitted from the light emission surface 6 are not uniform in the light emission surface 6. In addition, when the inclination directions of the reflection surface 7 have to be differentiated depending on their positions in order to make the light which is not emitted unidirectionally, be uniformly reflected in the vertical direction, the configuration of the reflection surface 7 becomes complicated. Therefore, it becomes difficult to design and manufacture the reflection surface and align the position of the reflection surface with the front light.
In addition, even when the configuration of the reflection surface 7 can be manufactured corresponding to the directions of the light of the point light source 12 emitted from the light emission surface 6, since an incident angle of the outside light such as sunlight is aligned in one direction, when the outside light is reflected by the reflection surface 7 whose inclination direction is varied in accordance with the front light using the point light source 12, the light is reflected by the reflection surface 7 in various directions so that brightness becomes uneven in the screen in the case of the outside light.